This invention relates to a method and apparatus for controlling the idle rotational speed of engines for driving automotive vehicles.
A known closed loop control method attempts to make the adjustment of the idle rotational speed of an automobile engine maintenance-free or to control the idle rotational speed so as to maintain a desired design value. When a throttle valve is closed, the deviation or difference between the actual idle rotational speed and the desired value is determined and the amount of air flow or the supply of mixture to the engine is controlled in accordance with the difference.
A disadvantage of this known control method is that no consideration is given to the compensation of a signal indicative of the desired value of the idle rotational speed for any automobile operating condition parameters. Consequently the closed loop control is always accomplished when the engine throttle valve is closed. As a result, a difficulty occurs when the vehicle is run while operating the engine at around the idle rotational speed, such as when the vehicle is run at a very low speed or when the foot brake is applied during the running of the vehicle to decelerate it. More specifically, since, in such a condition, the engine temperature has risen sufficiently and the warming-up of the engine has been completed so that the engine load, such as the viscosity resistance of the engine oil is decreased as compared with that at the idling operation during the warming-up period. If the desired value for the idle rotational speed is not compensated for changes occurring in the engine operating condition parameters, under such a running condition there is the danger of the engine rotational speed increasing abnormally against the will of the driver and causing a feeling of unpleasantness on the part of the driver.
Another disadvantage is that if, for example, any fault occurs in a rotational speed sensor for sensing the engine rotational speed, there is the possibility that the control amount computed in accordance with the sensor output signal will assume a value which is quite remote from a predetermined control range. Since this type of known control method sets no range of limits to the computed control amount, there is a disadvantage that during the running of an automobile there is the danger of the engine rotational speed varying abnormally against the will of the driver and causing a feeling of unpleasantness on the part of the driver.